Method and apparatus for making orthophotos using a fixed film bed

ABSTRACT

Method and apparatus for making substantially orthographic photo images from an optically projected stereo model of three dimensional terrain without necessitating quick precision movements of a relatively massive high inertia and precision machined film bed. A flexible fiber optic bundle is used to transmit light images from a first end to a second end. The first end is scanned in three dimensions over and upon the surfaces of the three dimensional stereo model while the second end is synchronously scanned in two dimensions over photo-sensitive material held in a relatively fixed and relatively cheaply constructed film bed. In a further embodiment, a first pseudoscanning cycle may be performed to obtain corresponding three dimensional digital scanning data for the first end of the fiber optic bundle which data are recorded and subsequently used to control a second automated real-scanning cycle where the film is actually exposed to either produce special effects such as color orthophotos or to merely permit more relaxed discontinuous operator control (including the ability to erase errors) during the first manually controlled pseudo-scanning cycle.

[22] Filed:

United States Patent 'Danko, Jr. et al.

METHOD AND APPARATUS FOR MAKING ORTHOPHOTOS USING A FIXED FILM BED [72]Inventors: Joseph 0. Danko, Jr., Baltimore,

Md.; Clinton J. T. Young, Alexandria, Va.

[73] Assignee: Danko Arlington, Inc., Baltimore,

Aug. 25, 1971 211 Appl.No.: 174,635

UNITED STATES PATENTS 3,244,893 5/1966 Miller ..356/2 X PrimaryExaminer-Samuel S. Matthews Assistant Examiner Michael D. HarrisAttorney-John W. Malley et a].

a 4x15 mm [451' Sept. 26, 1972 5 7] ABSTRACT Method and apparatus formaking substantially orthographic photo images from an opticallyprojected stereo model of three dimensional terrain withoutnecessitating quick precision movements of a relatively massive highinertia and precision machined film bed. A flexible fiber optic bundleis used to transmit light images from a first end to a second end. Thefirst end is Scanned in three dimensions over and upon the surfaces ofthe three dimensional stereo model while the second end is synchronouslyscanned in two dimensions over photo-sensitive material held in arelatively fixed and relatively cheaply constructed film bed. In afurther embodiment, a first pseudo-scanning cycle may be performed toobtain corresponding three dimensional digital Scanning data for thefirst end of the fiber optic bundle which data are recorded andsubsequently used to control a second automated realscanning cycle wherethe film is actually exposed to either produce special effects such ascolor orthophotos or to merely permit more relaxed discontinuousoperator control (including the ability to erase errors) during thefirst manually controlled pseudoscanning cycle.

23 Claims, 2 Drawing Figures HIW- MEL 7 I4! 17 1 5 PATENTEDSEPZSIQIZsumzorz INVENTORS J02? a lvmw, J (f/lwzA/ffw vq- ATTORNEYS METHOD ANDAPPARATUS FOR MAKING ORTHOPIIOTOS USING A FIXED FILM BED This inventiongenerally relates to a method and means for obtaining orthophotographsor planimetric i.e., orthographic) photo projections of threedimensional surfaces using optically projected stereo models thereof.Apparatus for achieving such results is generally referred to as anorthophoto instrument in the prior art.

The general art of making orthographic projections from opticallyprojected stereo models is relatively well known today after having beenintroduced in a potentially practical form in the l930s by a Frenchman,Robert Ferber and later developed to a greater degree by an American,Russell K. Bean of the U8. Geological Survey. General information aboutexisting orthophoto instruments may be obtained from various sources,for instance, the Manual of Photogrammetry published by the AmericanSociety of Photogrammetry, third edition, contains a discussion of priorart techniques and instruments for obtaining orthophotographs in sectionl7.l on pages 867 through 872.

Basically, an orthophoto instruments as previously known includesseveral basic elements (to be discussed in more detail below) alwaysused in conjunction with some means for vertically adjusting thepositionof a relatively massive and precisely machined film-holding bedwhich is expensive to manufacture andwhich ex- .hibits a rather highinertia thus inhibiting precisely accurate and rapid movements thereof.As will be more clearly apparent from the following discussion, suchmovements are often necessary to accurately produce the desiredorthophoto which requires accurately following the surface of theprojected three dimensional model.

i The basic operation of an orthophoto instrument will become moreapparent once the other basic elements of the orthophoto instrument areexplained.

In essence, the orthophoto instrument is used to ob tain anapproximately orthographic projection by exposing each elemental area ofa photosensitive film with a light image from a corresponding area thatis substantially upon the surface of an optically projectedthree-dimensional stereo model. The actual photographic printing is donewith only one of two projectors which are necessarily utilized foractually projecting the stereo model, as will be appreciated by those inthe art.

In order to accomplished this, a small scanning aperture" or slit(corresponding to the elemental area previously mentioned) iscontinuously scanned or moved in a predetermined raster along x and ycoordinates substantially in the plane of the photosensitive film whileother portions of the photosensitive film are shielded from lightexposure. Thus, the only light exposure to the photosensitive film isthrough the moveable aperture as it is being regularly scanned in acontinuous fashion along the x and y coordinates in the plane of thefilm. The operator then manually controls (directly or through servosystems) a vertical adjustment of the film-holder which of course alsocomprises the movable slit apparatus) to always keep the moving orscanning slit on the surface of the stereo model, or as nearly upon thesurface as is possible. In this manner, each elemental area of theresulting photo image has been effectively exposed by a correspondingarea upon the surface of the stereo model.

Usually, a blue light is used for projecting one of the stereo imagesand red light is used for projecting the other of the stereo imageswhich, together, form the stereo model of the terrain. (The operatoruses blue/red lens spectacles to keep stereo separation of the images aswill be appreciated.) In most conventional orthophoto instruments, thefilm is sensitive only to the blue light, thus, only the blue lightimage is actually utilized in obtaining a monochromatic orthophotoimage. Of course, the red light could be used instead if desired suchas, for instance, with infrared sensitive film.

After some thought reflection on this process, those in the art willreadily appreciate if they do not already) thatthe result issubstantially equivalent to an orthographic projection since each areaof the resulting photograph has been exposed at a level corresponding tothe actual surface of the stereo model. That is, the resultingphotograph is substantially equivalent to a true orthographic projectionof the particular terrain or other three dimensional surface of interestsuch that accurate quantitative measurements may now be made frompoint-to-point on the resulting orthophotograph which no longerincorporates the usual distortions caused by the tilt, relief, etc. ofthe terrain.

The particular scanning slot dimensions vary depending upon the rapidityof change in a particular terrain or surface of interest, the accuracyrequired in the finished orthophoto, etc. In conventional orthophotoinstruments, this slot is usually formed in a very thin viewing platenand the slot is then continuously scanned in a raster over the surfaceof the photosensitive film. Of course, this process in itself is quite aproblem since the slot is to be optimally placed as close to the filmsurface as possible and yet not so close as to actually damage the filmsurface. Furthermore, it must be controllably scanned in a raster withinvery accurate tolerances over the entire surface of a relatively large(typically 1 l X 14 inches or more) photosensitive film. To insure thatthe slot can be scanned in this manner, both the scanning mechanism andthe film-holding bed have had to be precisely machined. Furthermore, tohold the film properly a relatively massive film bed with vacuumchambers etc. has usually been provided.

Accordingly, such prior art orthopho instruments have been relativelyexpensive and complex devices. Besides having to provide means foraccurately and quickly moving a relatively massive film-holder in thevertical direction, additional means must be included on the movingfilm-holder to scan the exposure or scanning aperture over a ratherlarge film surface within a very close mechanical tolerance.

Using this invention, many of the disadvantages normally associated withthe construction of orthophoto instruments heretofore have now beeneliminated. Accordingly, orthophoto instruments constructed according tothe teachings of this invention and employing the methods of thisinvention are relatively easier and cheaper to build while yet providinga potentially superior final product.

Briefly, this invention provides a method and means for makingorthophotos without requiring the movement of a relatively massivefilm-holder or even a precision machined holder. Rather, a relativelylight-weight viewing platen having the scanning aperture therein isscanned in three dimensions over the optically projected stereo modeland with the slit being maintained substantially upon the surface of thestereo model. The light image passed by the scanning aperture is thenconducted through a coherent flexible fiber optic bundle to a fixedfilm-holding bed where the other end of the fiber optic bundle issynchronously scanned in two dimensions over the surface of thephotosensitive film using an air bearing interface therebetween. In thismanner, the scanning means for scanning in three dimensions is onlyrequired to move relatively lightweight simply constructed componentswhile the required elemental image from the surface of the stereo modelis conducted through the fiber optic bundle to a relatively stationaryphotosensitive film.

The aperture of the fiber bundle may be determined by its own dimensionsor by a mask that allows light to enter or leave it only through acertain area. This aperture normally will be of constant width over mostof its length but may vary, especially in the form of a tapered positionat each end; if exposures through these mined distance is easilymaintained between the stationary film and the movable end of the fiberoptic bundle while at the same time providing a virtually frictionlessbearing for such movement. Thus, the film itself does not have to be ina precisely planar disposition and there is thus no requirement for aprecision machined film bed.

Furthermore, a pseudo-scanning cycle may be carried out with no film inthe film-holder (or at least without permitting light to pass throughthe exit end of the fiberoptic bundle). During this pseudo-scanningcycle, the viewing platen is scanned over and upon the surfaces of thestereo model in the usual manner (i.e. with z axis position beingmanually controlled to keep the slot upon the stereo model surface)while digital (or analog) data representing the successive positions ofthe three dimensional scanning cycle are being recorded. Thereafter,film is inserted in the film-holder (and/or the exit-end of the fiberoptic bundle is uncovered for scanning in two dimensions over thefilmholder in synchronism with the three dimensional scanning of theentrance end of the fiber optic bundle) and the pre-recorded digitaldata are then utilized by conventional numerical control techniques toautomatically control a second real scanning cycle wherein the film isactually exposed to produce the desired orthophoto. In this manner, theoperator may perform a discontinuous scanning cycle in the firstpseudo-scan while the second real scan is actually continuous in natureto insure even photographic exposure times, etc. over the entireorthophoto. Thus, the operator does not have to concentrate so hard onthe first pseudo-scan and/or he may back up and erase certain of thedata if he detects that an error has been made.

The printing may be performed as in the prior art by using blue lightsensitive film in conjunction with blue and red projected stereo halfimages. Alternatively, two mutually exclusive types of polarized lightmay be utilized (such as plane polarized, circularly polarized to obtainthe necessary stereo separation so that the operator can view (throughspectacles with lenses that separate the images appropriately) theactual stereo model in controlling the vertical position of the scanningaperture during a scanning cycle thus permitting white light (of apredetermined polarization as determined by an appropriate filter) to beused for printing and thus the possibility of producing a colororthophoto if desired. Moreover, when the pseudoscanning and realscanning in a later automated scanning cycle steps are utilized, one ofthe two stereo projectors can actually be turned off while the otherprojector projects white light for printing in the real scan cyclethereby permitting a true color orthophoto to be made regardless ofwhether red and blue or polarized light is utilized to obtain thenecessary stereo model during the initial pseudo-scan where thenecessary operator action requires the existence of the actual stereomodel for adjusting the vertical position of the scanning aperture.

The vertical adjustment of the scanning aperture may be made directly bymanually operated means or by available automatic three dimensionalscanning means. On the other hand, a remote servo-controlled unit may beused for controlling the vertical adjustment such that the operator mayhave a separate hand-held manually controlled servo unit for adjustingthe vertical position.

Other objects and advantages of this invention will become more apparentfrom the following detailed description and accompanying drawings, ofwhich:

FIG. 1 is a partially pictorial and partially schematic diagram of anoverall orthophoto instrument constructed according to this inventionand utilizing the method of this invention; and

FIG. 2 is a close-up pictorial view of a portion of the movable means ofthe orthophoto instrument shown in FIG. 1.

Referring to FIG. 1, a complete orthophoto instrument constructedaccording to this invention is shown which utilizes the method of thisinvention.

Most of the essential elements are located within a fixed frame 10having a projection means generally indicated by numeral 12 and which islocated at the upper portion of the frame 10. A movable mounting meansgenerally indicated by numeral 14 is disposed in the general mid-sectionof the frame 10 and a filmholding means 16 such as a vacuum chamber isdisposed at the lower portion of frame 10. A flexible optical imageconducting means 18 is shown as being connected between a viewing platen20 at one end and a film scanning holder 22 at the other end. Theviewing platen 20 is movable in three dimensions to scan the first endof the fiber optic bundle 18 upon the surface of the three dimensional(x, y, 2) stereo model (provided by the projection means) while theholder 22 is linked rigidly to the movable mounting means forsynchronous movement in two dimensions (x, y) of the other end of thefiber optic bundle over the surface of a photosensitive film 24. Thefilm is generally maintained beneath a light-tight film cover 26 whichmay comprise, for instance, black light-opaque cloth or the like.

The black opaque light stop 26 actually covers the holder 22 and thesecond end of the fiber optic bundle 18 but it is shown as being cutaway at 28 in FIG. 1 for the purposes of illustration.

As those in the art will no doubt readily appreciate, the projectionmeans 12 comprises conventional projectors 30 and 32 for projectinglight through predetermined halves of transparent photo images negativesor positives) held in holders 34 and 36, i.e., to project complimentaryimages of a stereo pair. The transparencies held by holders 34 and 36have been taken from two different perspectives or vantage points as,for instance, from an airplane at two different points along apredetermined path of travel as will be appreciated by those in the art.The projectors 30 and 32 are each gimbaled about respective conventionallens systems 38 and 40 which are, in turn," mechanically coupled throughtelescoping arms 42 and 44 respectively to an attaching structure thatmoves with the viewing platen 20. The attaching structure associatedwith the viewing platen 20 is gimbaled to permit free movement of theplaten itself in the mid-section region of the frame without binding thetelescoping arms 42 and 44. The telescoping arms will, however, keep thegimbaled projectors 30 and 32 properly oriented at all positions withrespect to the transparent stereo images so that a proper stereo modelin three dimensions (when viewed by an operator using special spectaclesto keep the "necessary left/right eye-image separation) is opticallyprojected into the mid-region of frame 10, as will be appreciated bythose in the art.

In essence, the projection means 12 comprises any of the usualconventional projection means for forming three dimensional stereomodels such as are commonly used on stereo plotters for plottingconstant elevation lines, etc. from such stereo models. In actualpractice, a third projector may be included on the right-hand side offrame 10 to permit the setting up of two contiguous three dimensionalstereo models (on the left and right side of the frame 10 respectively)so that plotting may be continuously carried out from one end to theother of the frame, as will be appreciated by those in the art.

The mid-section or movable mounting means 14 generally comprises aplaten which is vertically adjustable on parallel rods 46 and 48 byvirtue of either hand-operated cranks 50, 90 or a remote controlledmotor 52. Either the hand-cranks 50, 90 or the motor 52 will result in arotation of shaft 54 which is keyed to the pinion of a rack and pinionmechanical adjustment for obtaining vertical movement of platform 56upon which platform the scanning aperture 20 is mounted. Of course, alead screw z axis adjustment could also be utilized as could many otherpossible mechanical adjustment systems.

This movement in the vertical direction i.e. along the z axis) isnecessary to keep the scanning aperture in the surface of the threedimensional model as the platen is being translated in a predeterminedscan raster along the x and y axis directions. Movement along the y axisdirection is obtained by moving platform 58 along parallel rods 60 and62 through a rotation of lead screw 64. The lead screw 64 is rotated bya motor 66 and by virtue of the threadable connection at 68 withplatform 58, the whole platform 58 (including its component,the'vertically adjustable platform 56) is then translated along the yaxis direction at a speed determined by the motor 66 and the pitch ofthe lead screw 64 as will be apparent to those in the art.

Movement in the mutually perpendicular x axis direction is obtained bymoving the frame 70 along rods 72 and 74 by virtue of a lead screw 76which is threadably attached to the frame 70 at 78 and rotated by motor80. As before, the movement in the x direction is determined by thespeed of motor 80 and the pitch of the lead screw 76 as will be apparentto those in the art. As shown in FIG. 1, the platform 58 which istranslated along the y axis direction is itself carried within the frame70 which is translatable along the x direction. Furthermore, thevertically adjustable platform 56 is mounted upon the platform 58.Accordingly, by properly controlling the motors 66 and 80, the platform58 may be scanned (and hence the scanning aperture on viewing platen 20)in a regular scan raster along the x and y axis directions as should nowbe apparent. Furthermore, as such a scan raster is traversed, thevertical position of the viewing platen 20 may be adjusted by hand-wheel50 or motor 52 to keep the scanning aperture of the viewing platen uponthe surface of the stereo model.

To make the x, y scan raster completely automatic, limit switches 82 and84 are mounted to detect the endof-travel in the left and rightdirections along the x axis motion while limit switches 86 and 88 aremounted to detect the end of travel in the y axis directions. As shouldnow be apparent to those in the art, a completely automatic x-y scanraster may be performed by first, causing the motor 66 to operate at aconstant speed in a given direction until the limit switch for motion inthat direction is actuated, whereupon the direction of the motor 66 isreversed while the speed is again maintained at the same constant value.Thereafter, the end-of-travel detector for movement in the new directionis connected to cause subsequent reversal of the motor direction back toits initial direction, etc., thus continuously cycling the platform 58back and forth on rods 60 and 62 in the y axis directions at a constantspeed. Furthermore, each time one of the end-of-travel detectors 86 or88 is actuated, the motor 80 should be energized momentarily for apredetermined number of rotations of lead screw 76 thus traversing thecarriage or frame 70 along rods 72 and 74 for a predetermined distancecorresponding to the scanning aperture dimensions as should be apparentto those in the art.

in some cases, it may be desirable to scan at other than constant speed.For instances, if a model contains a great deal of variation of heightin some areas and little in others, the operator in reading andrecording data in a pseudo-scan may wish to use a higher traverse speedin the flatter areas than in those with more rapid height changes.Again, in exposing the film, controlled variations "in scanning speedmay be used to equalize exposure, connecting for variations in densityin the picture transparency.

The vertical adjustment of platform 56 may be obtained by manuallymanipulating wheel 50 when on the far side of the machine and wheel 90when on the near side of the machine as shown in FIG. 1. By virtue ofthe reversing gears 92, 94, the same relative directions or rotations ofwheels 50 and 90 will result in vertically ascending or descendingmovements of platform 56 regardless of which side is used by theoperator. Furthermore, the movements in the vertical direction ofplatform 56 may be achieved remotely by properly energizing motor 52from a hand-held transmitter 96. If desired, a switch might be includedfor reversing the direction of the motor 52 depending upon theparticular side of the machine where the operator happens to be thusmaintaining the same directions of rotation for the hand-held unit withrespect to ascending or descending movements of the platform 56. Forinstance, the motor 52 and the hand-held transmitter 96 may compriseconventional electrical selsyn motor transmitter/receiver units as willbe appreciated by those in the art.

Platform 58 which is translated in the scan raster along the x and ycoordinate directions includes a rigidly attached arm 100 which isutilized for moving the holder 22 in a synchronous fashion along thedesired x-y scan raster over the film surface 24. The holder 22 and arm100 move back and forth in the y direction with corresponding movementsof platform 58 and within a channel formed by guides 102 and 104 in thelight opaque covering 26. Furthermore, the channel formed by guides 102and 104 is itself translatable in the x direction by virtue of the factthat the light opaque screen 26 is itself movable over rollers 106 and108 at either end of the film-holder 16 as shown in FIG. 1. Aspreviously mentioned, the entire film surface 24 is actually covered bythe light opaque screen 26,to prevent light exposure of the film 24except through the exit end of the fiber optic light image conductingbundle 18 as should now be apparent.

'A portion of the movable mounting means 14 is shown in more detail atFIG. 2.

Here, the vertically adjustable platform 56 is shown mounted on rods 48and 46 which are movable through precision ball-bushings 150 and 152mounted in platform 58. Actually, there is a third ball-bushing hiddenfrom view in FIG. 2 to provide a three point rigid mounting for theplatform 56 on rods 46, 48. The vertical adjustment, as previouslyexplained, is obtained by rotating shaft 54. Shaft 54 is keyed (usingkeyway 154 as shown in FIG. 2) so that pinion 156 is free to slide alongthe shaft 54 in the y direction whileyet being rotatably rigid by virtueof the keyway 154. Thus, when the shaft 54 is turned, the pinion gear156 is likewise turned and by virtue of its engagement with rack gear158, the platform 56 is vertically adjusted as should be apparent. Themovement of platform 58 in the y direction is by virtue of movementthrough ballbushings 160 and 162 in the platform 58 through which rods60 and 62 respectively passed. Actually, there is a third ball-bushinghidden from view in FIG. 2 to provide a three point rigid mounting forthe platform 58 upon the rods 60 and 62.

' The fiber optic bundle 18 is shown in FIG. 2 comprising asubstantially rectangular cross-sectioned bundle of many opticallyconducting fibers having a first end 164 which is exposed in an aperture166 in the viewing platen 20. The fiber optic bundle 18 isconventionally available from such sources as the American OpticalCorporation, Southbridge, Mass. Generally, such flexible imageconducting means comprises thousands of clad light conducting fibersthat are fused together to form a bundle or rod, that is capable oftransmitting a light image from one end to the other with onlyacceptable losses in intensity and/or resolution. Of course, thescanning aperture permits effective use of only a desiredcross-sectional area of the bundle as should be apparent.

The image passing through the scanning aperture 166 is then conducted bythe fiber optic bundle 18 down to its second end generally indicated as172 in FIG. 2. (The actual end is hidden from view.)

Since the arm is rigidly attached to the platform 58 and since theplatform 58 is scannable along a raster in the x-y coordinate directionsas previously discussed, it follows that the arm 100 and the holder 22for the second end of the fiber optic bundle 18 will similarly bescanned along a raster in two coordinate directions, namely, the x-ycoordinates.

The length of arm 100 is effectively adjusted by bolt 174 and slot 176which adjustably secure a lower extension l78 to the upper portion ofarm 100 as should be apparent from FIG. 2. However, this adjustment isonly a rough one and not intended to be the final positioningdeterminant for the second end face or exit end of the fiber opticbundle 18. Rather, a second arm 180 projects horizontally from arm 100and is freely movable at bearing 182 to provide vertical movement at theopposite end of arm 180 where a holder 184 accurately maintains theposition of the second end face of the fiber optic bundle 18 withrespect to arm 100 in the x and y coordinate directions. Of course, thewhole arm 100 is translated according to the scan raster in the x and ydirections as previously noted thus causing the second end of the fiberoptic bundle to be scanned in two dimensions in the x-y direction asshould now be apparent.

Furthermore, the vertical adjustment of the second end of fiber opticbundle 18 is critical only insofar as it should be maintained at arelatively constant height above the film surface 24 but yet not soclose thereto that it actually damages the film surface. A veryimportant reason for controlling separation between the end of the fiberoptic bundle and the fiber is the fact that light diverges rapidly fromthe end of each fiber. There fore, image quality will be reduced if theseparation is so large that any point receives much light from more thanone fiber. This problem is readily apparent to those skilled in the art.The object of controlling separation is achieved by providing an airbearing in holder 184. That is, air is input at 186 under a suitablepressure and output at one or more openings of the bot tom side ofholder 184 to provide a cushion of air having predetermined dimensionsbetween the bottom of holder 184 and the top of the film surface 24. Inthis manner, slight adjustments are made for the second end of the fiberoptic bundle 18 to maintain a predetermined distance above the surfaceof the film while translating thereover in the xy coordinate raster.

Instead of the laterally projecting hinged arm 180 for permittingvertical adjustment of the exit end of fiber optic bundle 18, othermeans could be used. For instance, a telescoping mechanical connectionthat is rigid in x-y directions but freely slidable but not rotatable inthe z direction could be provided to permit 2 direction adjustments ofthe air bearing cushioned holder for the exit end of fiber optic bundlel8.

Referring back to FIG. 1 it will be noted that electrical connectionsfrom the end-of-travel sensors 82, 84, 86 and 88 as well as the x and yaxis coordinate motors 80 and 66 respectively are connected via wires a,b, c, d, e and f, respectively to a conventional automatic scan controlunit 200. The scan control unit 200 may be of conventional design quitesimilar to those in the prior art used for translating the scanning slitin the actual plane .of the film while the whole film bed itself wasbeing vertically adjusted. For instance, the end-oftravel sensors maycompromise conventional limit switches which are, in turn, electricallyconnected to corresponding conventional latching relays or flip-flops orthe like in-scan control unit 200 which are interconnected to result ina pre-programmed automatic scan raster along the x and y coordinates.That is, each time an end-of-travel detector is activated, the.direction of travel along the corresponding coordinate axis is reversedfor motor 66 and end-of-travel detectors 84 and 88. Furthermore, eachtime such a reversal occurs, motor 80 is temporarily energized orstepped or otherwise activated to cause lead screw 76 to advance thecarriage or frame 70 a predetermined distance cor responding to thedimensions of the scanning aperture in the x direction. The limitswitches 82 and 86 may be utilized to cause automatic reversal of motor80 in a similar fashion although, for practical purposes, the carriage70 will usually begin at one extreme end of the frame 10 and traverse insuccessive steps to the other extreme end with a step being taken eachtime a complete traverse of platform 58 is completed in the y coordinatedirection as should now be apparent. Accor'dingly, the limit switches 82and 86 are not absolutely essential except for starting and stopping thecomplete scanning cycle.

In addition, electrical connection g from motor 52 is connected throughan optional remote z axis control unit 202 to a hand-held transmitter 96as previously indicated. Thus, when the remote z axis control unit 202is turned on, the hand-held transmitter 96 may be used in lieu of thehand operated wheels 50 and 90. As previously discussed, the reversingswitch 204 may be incorporated in this control unit to reverse thedirection of motor 52 as a function of the operators position.

Additionally, a conventional digital ,or numerical machine control unit206 may also be incorporated in the orthophoto instrument of thisinvention. Such a system is particularly advantageous to reduce thenecessary operator attention and to produce special effects such ascolor orthophotos, etc. as will soon become more apparent.

When the digital control unit 206 is utilized, two related scanningcycles are effected. A first scanning cycle may be termed a pseudo-scan"wherein the platen 20 and its scanning aperture are scanned as in theusual fashion along three dimensions but where now the motors 80, 66 and52 are utilized as transmit ters or generators to indicate the relativex, y and z coordinates respectively of the scanning aperture. Thisinformation is input from the automatic scan control unit 200 and fromthe electrical connection g to a conventional digital recording devicewhich digitizes and records data representing the successive threedimensional coordinates utilized in scanning upon the surface of thestereo model. By properly controlling the recording equipment, theoperator may stop and rest occasionally to effect a rather discontinuoustype of pseudoscanning operation which will not be reflected in therecorded information since the recording device will be effectivelydeactivated during the operators temporary rest period. Furthermore, ifthe operator determines that he has just made an error he may back upand retrace that particular portion of the scanning cycle to replace thejust recorded faulty digital information with accurate information.During this pseudo-scan, there is either no film 24 in the film holder16 or the lower portion of arm is moved so that the passage of light isblocked so that it is not carried to the film 24 through the fiberbundle 18. in this manner, no matter how often the operator rests or howoften he makes mistakes and corrects those mistakes, no film will beexposed and hence wasted. Accordingly, the operator can take his time inthis pseudo-scan to make certain that the vertical position of platen 20is exactly on the surface of the stereo model at each point in theraster scan'to obtain a more perfect tracing of the three dimensionalmodel. Thereafter, the recorded digital coordinate information is playedback and utilized with conventional-control apparatus to control themovements of motors 80, 66, and 52. respectively to reproduce exactlythe recorded scanning pattern in a second real-scan wherein the fiberoptic bundle l8 and arm 100 are in proper operating position (orobstruction to light passage is removed) and a sheet of photosensitivefilm 24 is in film-holder 16 to result in an actual printing of thedesired orthophoto.

Of course, during the pseudo-scan it is necessary that the proper stereoimage separation be maintained to result in the operator seeing thenecessary stereo image or model of the terrain. However, during thesecond real scan operation it is not actually necessary for the threedimensional model to be in existence but rather, only one of theprojectors 30 and 32 needs to be energized. If, as with the conventionalorthophoto instruments, one of the stereo images is formed with bluelight and the other with red light and the film is sensitive only to theblue light then of course, it is not absolutely necessary to turn offone of the projectors since the film will only respond to the bluelight. Furthermore, polarized light can be similarly used whereappropriate steps are taken to insure that polarized light from only onestereo image is actually utilized in printing the orthophoto on thephotosensitive material 24. Moreover, it is possible to utilize only oneof the projectors without any color filters or polarizing filters, etc.to project a white light image for printing a color orthophoto on thephotosensitive material 24 as previously discussed.

Accordingly, this invention provides both an apparatus and method forobtaining orthophotos in a simpler and more efficacious manner thanpreviously possible with prior art orthophoto instruments. A massivefilm bed does not have to be moved with this invention nor does the filmbed itself have to be made with such precision to hold the film in anexact planar position as with the prior art machines since the exit endof the light fiber bundle 18 is free to adjust its vertical position toslight changes in the plane of the film while yet being maintained at aproper predetermined distance from the film surface. Rather, only therelaill tively light-weight platform 56 with the viewing platen andscanning aperture needs to be vertically moved during the scan rasteralong the x and y coordinates. This permits the operator to quicklyadjust the vertical or z axis direction movements in response to rapidchanges in terrain topography, etc. as should be apparent to those inthe art. Furthermore, this invention permits color printing oforthophotos by several different techniques and, because there is noneed to move the entire film bed up and down, etc. larger sheets of filmmay be utilized to obtain larger magnification factors in resultingoriginal orthophotonegatives. In addition, a conventional digitalnumerical control unit may be used to permit discontinuous plotting in afirst pseudo-scan followed by a real scan cycle where the actualorthophoto negative is printed.

If desired, the data taken during the pseudo-scanning cycle may be inanalog rather than digital form. ln this case, conventional analogrecording equipment would be utilized to record analog data representingthe coordinate positions of the threedimensional pseudo-scan. Therecorded analog data are then used in analog data control techniques tocause the motors to retrace the model in a real scanning cycle, asshould now be appreciated by those skilled inthe art.

The use of fiber optics has been described as a preferred means ofallowing for variation in the z dimension between the optical modelcontour and the photographic film. It will be apparent to those skilledin the art that this can be accomplished by other means such as a trainof reflecting surfaces and one or more lenses or a lens system ofconstant magnification but variable overall length.

While only a few embodiments of this invention have been particularlydescribed in the above specification, those skilled in the art willreadily appreciate that these embodiments are only intended to beexemplary of possible methods and apparatus for achieving practicalresults with the invention. Many obvious modifications may be made tothe exemplary embodiments without materially altering the statedfunctions, purposes and objectives of this invention. Accordingly, allsuch modifications are intended to be included within the scope of thisinvention.

What is claimed is:

1. An orthophoto instrument for plotting substantially orthographicprojections of three dimensional surfaces using an optically projectedthree dimensional stereo model of the surface, said instrumentcomprising:

projection means for optically projecting said three dimensional stereomodel,

flexible optical image conducting means having a predetermined effectivecross-sectional area for conducting optical images therethrough from afirst end to a second end thereof,

film-holding means for holding a surface of a photosensitive material ina predetermined position, and

movable mounting means connected to the flexible optical imageconducting means for effecting three dimensional scanning of said firstend over and substantially upon the surfaces of said three dimensionalstereo model while effecting synchronous simultaneous two dimensionalscanning of said second end over the surface of said photosensitivematerial thereby plotting said orthographic projection thereon.

2. An orthophoto instrument as in claim 1 further comprising automaticscanning means for automatically effecting synchronous scanning of thefirst and second ends along at least two of the three dimensionalcoordinate directions.

3. An orthophoto instrument as in claim 1 further comprising:

digitizing and recording means for recording digital data representingsuccessive three dimensional positions of said first end during a firstpseudoscanning cycle wherein at least one dimensional coordinateposition is manually determined to keep said first end substantiallyupon thesurfaces of said three dimensional stereo model, and

digital control means for utilizing such recorded digital data in asecond automatically controlled real scanning cycle wherein the desiredorthographic projection is actually printed onto the photosensitivematerial.

4. An orthophoto instrument as in claim 1 wherein said movable mountingmeans includes air bearing means for holding said second endsubstantially at a predetermined distance from the photosensitivematerial during scanning thereof.

5. An orthophoto instrument as in claim 1 wherein said predeterminedeffective cross-section is substantially rectangular at both said firstand second ends.

6. An orthophoto instrument as in claim 1 wherein said first end ismounted in alignment with an aperture in a viewing platen.

7. An orthophoto instrument as in claim 1 wherein said movable mountingmeans comprises three members, each being relatively adjustable in adirection substantially orthogonal to that of the other members.

8. An orthophoto instrument as in claim 1 further including:

xy scanning means for automatically scanning said first and second endsin a predetermined x--y raster along orthogonal x and y axis directionsin two dimensions, and

z adjustment means for moving said first end along a z axisperpendicular to both said x and y axis.

9. An orthophoto instrument as in claim 8 wherein said 2 adjustmentmeans is manually operable.

10. An orthophoto instrument as in claim 9 wherein said 2 adjustmentmeans is manually operable through a remote control hand-held unit.

11. An orthophoto instrument for plotting orthographic projections fromoptically projected three dimensional stereo models, said instrumentcomprising:

projection means for optically projecting said three dimensional stereomodel,

a stereo model viewing platen having an aperture therein,

mounting means for adjustably positioning said viewing platen alongthree dimensions in the region of said stereo model,

optical image conducting means connected at one end to said platen forconducting therefrom an optical image passing through said aperture andcorresponding to a selected portion of said stereo model as determinedby the position of said platen,

film-holding means for holding a photosensitive material, and

film exposing means connected to the other end of said optical imageconducting means and rigidly associated with at least part of saidmounting means for synchronous movement of the said other end withrespect to said platen in two dimensions over said film-holding meanswhereby an orthographic projection may be obtained on saidphotosensitive material by scanning the aperture in said two dimensionsand simultaneously adjusting said platen in the remaining thirddimension to substantially maintain the apertureon the surface of saidstereo m'odel.

12. An orthophoto instrument as in claim 11 further comprising automaticscanning means for automatically moving said platen aperture and saidfilm exposing means in a constant. rate raster scanning motion back andforth along one of said two dimensions with successive end-oftravelindexing movements along the other one of said two dimensions.

13. An orthophoto instrument as in claim 11 wherein said mounting meanscomprises:

a platform mounted within a first frame, said platform being slidablypositioned on two parallel elongated means oriented along one of saidtwo dimensions,

a first lead screw mounted within said first frame and connected to saidplatform for effecting platform movement along said parallelelongated-means by rotation of said first lead screw,

said first frame being mounted within a second frame and along-beingslidably positioned on two further parallel elongated means orientedalong the other one of said two dimensions,

a second lead screw mounted within said second frame and connected tosaid first frame for effecting first frame movement along said furtherparallel elongated means by rotation of said second lead screw,

a further platform mounted on said first-mentioned platform for carryingsaid platen, and

vertical positioning means connected between both of said platforms foreffecting desired positions adjustments of said platen in the thirddimension.

14. An orthophoto instrument as in claim 13 further comprising:

first motor means connected for rotating said first lead screw,

second motor means connected for rotating said first lead screw, I

end-of-travel detector means for detecting when predetermined movementlimits have been reached for at least one of said two dimensions, and

automatic scan means connected to said first and second motor means andto said end-of-travel detector means for effecting automatic coordinateenergization of each of the motor means to obtain an automatic rasterscan of said aperture over a predetermined area in said two dimensions.

15. An orthophoto instrument as in claim 12 wherein said verticalpositioning means comprises a manually operated rack and pinion geararrangement.

16. An orthophoto instrument as in claim 12 wherein said verticalpositioning means comprises a remote controlled electromechanicaladjustment means.

17. An orthophoto instrument as in claim 16 wherein saidelectromechanical adjustment means comprises an electrical servo motor.

18. An orthophoto instrument as in claim 12 wherein said verticalpositioning means comprises both direct manually operated means andremotely controlled electromechanical means. together with selectionmeans for permitting either mode of vertical adjustment to be used.

19. An orthophoto instrument as in claim 11 further comprising:

digital recording means for recording digitized signals representingsuccessive three dimensional positions of said aperture during a firstthree dimensional pseudo-scanning cycle where at least the thirddimension position adjustment is effected by manually controlled means,and

digital control means for automatically effecting a second continuousthree dimensional real scanning cycle in accordance with the recordeddigitized signals whereby the first pseudo-scanning cycle may be carriedout without photosensitive material in the film-holding machine and evenin a discontinuous fashion if desired while the second continuous realscanning cycle is then carried out with photosensitive material toresult in the desired orthophoto.

20. An orthophoto instrument as in claim 11 wherein said film exposingmeans comprises:

a holder for positioning the surface of said other end of said opticalimage conducting means in a plane that is substantially parallel to theplane of the photosensitive material,

said holder being freely movable in a direction perpendicular to theplane of the photosensitive material, and

said holder including air bearing means for providing an air bearing ofsubstantially predetermined dimensions between said surface of the otherend and said photosensitive material whereby the film exposing means isfreely translatable over the photosensitive material at a predetermineddistance therefrom.

21. An orthophoto instrument as in claim 11 wherein said optical imageconducting means comprises a flexible coherent bundle of opticallyconducting fibers, said bundle having a generally rectangular overallcross-section at the ends thereof.

22. A method for plotting orthographic projections using an opticallyprojected three dimensional stereo model, said method comprising thesteps of:

projecting an optical three dimensional stereo image,

scanning a first end of an optical image conducting means having apredetermined effective cross-sectional area in three dimensionssubstantially along and upon the three dimensional surfaces of saidstereo image, and

synchronously scanning a second end of said optical image conductingmeans in two of said three dimensions over the surface of aphotosensitive material.

23. A method as in claim 22 wherein said first mentioned scanning stepis performed in conjunction with a step of digitally recording datarepresenting the successive three dimensional scanning positions andwherein said synchronously scanning step is thereafter auto-

1. An orthophoto instrument for plotting substantially orthographicprojections of three dimensional surfaces using an optically projectedthree dimensional stereo model of the surface, said instrumentcomprising: projection means for optically projecting said threedimensional stereo model, flexible optical image conducting means havinga predetermined effective cross-sectional area for conducting opticalimages therethrough from a first end to a second end thereof,film-holding means for holding a surface of a photosensitive material ina predetermined position, and movable mounting means connected to theflexible optical image conducting means for effecting three dimensionalscanning of said first end over and substantially upon the surfaces ofsaid three dimensional stereo model while effecting synchronoussimultaneous two dimensional scanning of said second end over thesurface of said photosensitive material thereby plotting saidorthographic projection thereon.
 2. An orthophoto instrument as in claim1 further comprising automatic scanning means for automaticallyeffecting synchronous scanning of the first and second ends along atleast two of the three dimensional coordinate directions.
 3. Anorthophoto instrument as in claim 1 further comprising: digitizing andrecording means for recording digital data representing successive threedimensional positions of said first end during a first pseudo-scanningcycle wherein at least one dimensional coordinate position is manuallydetermined to keep said first end substantially upon the surfaces ofsaid three dimensional stereo model, and digital control means forutilizing such recorded digital data in a second automaticallycontrolled real scanning cycle wherein the desired orthographicprojection is actually printed onto the photosensitive material.
 4. Anorthophoto instrument as in claim 1 wherein said movable mounting meansincludes air bearing means for holding said second end substantially ata predetermined distance from the photosensitive material duringscanning thereof.
 5. An orthophoto instrument as in claim 1 wherein saidpredetermined effective cross-section is substantially rectangular atboth said first and second ends.
 6. An orthophoto instrument as in claim1 wherein said first end is mounted in alignment with an aperture in aviewing platen.
 7. An orthophoto instrument as in claim 1 wherein saidmovable mounting means comprises three members, each being relativelyadjustable in a direction substantially orthogonal to that of the othermembers.
 8. An orthophoto instrument as in claim 1 further including:x-y scanning means for automatically scanning said first and second endsin a predetermined x-y raster along orthogonal x and y axis directionsin two dimensions, and z adjustment means for moving said first endalong a z axis perpendicular to both said x and y axis.
 9. An orthophotoinstrument as in claim 8 wherein said z adjustment means is manuallyoperable.
 10. An orthophoto instrument as in claim 9 wherein said zadjustment means is manually operable through a remote control hand-heldunit.
 11. An orthophoto instrument for plotting orthographic projectionsfrom optically projected three dimensional stereo models, saidinstrument comprising: projection means for optically projecting saidthree dimensional stereo model, a stereo model viewing platen having anaperture therein, mounting means for adjustably positioning said viewingplaten along three dimensions in the region of said stereo model,optical image conducting means connected at one end to said platen forconducting therefrom an optical image passing through said aperture andcorresponding to a selected portion of said stereo model as determinedby the position of said platen, film-holding means for holding aphotosensitive material, and film exposing means connected to the otherend of said optical image conducting means and rigidly associated withat least part of said mounting means for synchronous movement of thesaid other end with respect to said platen in two dimensions over saidfilm-holding means whereby an orthographic projection may be obtained onsaid photosensitive material by scanning the aperture in said twodimensions and simultaneously adjusting said platen in the remainingthird dimension to substantially maintain the aperture on the surface ofsaid stereo model.
 12. An orthophoto instrument as in claim 11 furthercomprising automatic scanning means for automatically moving said platenaperture and said film exposing means in a constant rate raster scanningmotion back and forth along one of said two dimensions with successiveend-of-travel indexing movements along the other one of said twodimensions.
 13. An orthophoto instrument as in claim 11 wherein saidmounting means comprises: a platform mounted within a first frame, saidplatform being slidably positioned on two parallel elongated meansoriented along one of said two dimensions, a first lead screw mountedwithin said first frame and connected to said platform for effectingplatform movement along said parallel elongated means by rotation ofsaid first lead screw, said first frame being mounted within a secondframe and along being slidably positioned on two further parallelelongated means oriented along the other one of said two dimensions, asecond lead screw mounted within said second frame and connected to saidfirst frame for effecting first frame movement along said furtherparallel elongated means by rotation of said second lead screw, afurther platform mounted on said first-mentioned platform for carryiNgsaid platen, and vertical positioning means connected between both ofsaid platforms for effecting desired positions adjustments of saidplaten in the third dimension.
 14. An orthophoto instrument as in claim13 further comprising: first motor means connected for rotating saidfirst lead screw, second motor means connected for rotating said firstlead screw, end-of-travel detector means for detecting whenpredetermined movement limits have been reached for at least one of saidtwo dimensions, and automatic scan means connected to said first andsecond motor means and to said end-of-travel detector means foreffecting automatic coordinate energization of each of the motor meansto obtain an automatic raster scan of said aperture over a predeterminedarea in said two dimensions.
 15. An orthophoto instrument as in claim 12wherein said vertical positioning means comprises a manually operatedrack and pinion gear arrangement.
 16. An orthophoto instrument as inclaim 12 wherein said vertical positioning means comprises a remotecontrolled electromechanical adjustment means.
 17. An orthophotoinstrument as in claim 16 wherein said electromechanical adjustmentmeans comprises an electrical servo motor.
 18. An orthophoto instrumentas in claim 12 wherein said vertical positioning means comprises bothdirect manually operated means and remotely controlled electromechanicalmeans together with selection means for permitting either mode ofvertical adjustment to be used.
 19. An orthophoto instrument as in claim11 further comprising: digital recording means for recording digitizedsignals representing successive three dimensional positions of saidaperture during a first three dimensional pseudo-scanning cycle where atleast the third dimension position adjustment is effected by manuallycontrolled means, and digital control means for automatically effectinga second continuous three dimensional real scanning cycle in accordancewith the recorded digitized signals whereby the first pseudo-scanningcycle may be carried out without photosensitive material in thefilm-holding machine and even in a discontinuous fashion if desiredwhile the second continuous real scanning cycle is then carried out withphotosensitive material to result in the desired orthophoto.
 20. Anorthophoto instrument as in claim 11 wherein said film exposing meanscomprises: a holder for positioning the surface of said other end ofsaid optical image conducting means in a plane that is substantiallyparallel to the plane of the photosensitive material, said holder beingfreely movable in a direction perpendicular to the plane of thephotosensitive material, and said holder including air bearing means forproviding an air bearing of substantially predetermined dimensionsbetween said surface of the other end and said photosensitive materialwhereby the film exposing means is freely translatable over thephotosensitive material at a predetermined distance therefrom.
 21. Anorthophoto instrument as in claim 11 wherein said optical imageconducting means comprises a flexible coherent bundle of opticallyconducting fibers, said bundle having a generally rectangular overallcross-section at the ends thereof.
 22. A method for plottingorthographic projections using an optically projected three dimensionalstereo model, said method comprising the steps of: projecting an opticalthree dimensional stereo image, scanning a first end of an optical imageconducting means having a predetermined effective cross-sectional areain three dimensions substantially along and upon the three dimensionalsurfaces of said stereo image, and synchronously scanning a second endof said optical image conducting means in two of said three dimensionsover the surface of a photosensitive material.
 23. A method as in claim22 wherein said first mentioned scanning step is performed inconjunction with a step of digitally recording data representiNg thesuccessive three dimensional scanning positions and wherein saidsynchronously scanning step is thereafter automatically carried outsimultaneously with an automatic repeat of the first mentioned scanningstep using the digitally recorded data to cause an automatic scan ofboth ends of the optical image conducting means.